This invention relates in general to gas or pollutant testing devices and in particular to a new and useful device for detecting gases which must first be treated to form reaction products that lead to a distinct color in a following indicator material.
This invention particularly concerns a test tube with several reagent layers affecting the detection reaction, that are separated from one another by a permeable interlayer.
Test tubes with several reagent layers are used particularly for cases in which the successive layers bring about a stepwise reaction of the pollutant to be detected until a colorimetric evaluation is ultimately made accessible in an indicator layer, and also to test tubes in which the degree of color of the indictor layer is compared with a color comparison layer and is thus evaluated.
To detect various gaseous pollutants, it is necessary to convert them first in a preliminary layer into reaction products that lead to a distinct color in a following indicator layer. A test tube of this type has been disclosed by German Patent Application Disclosure No. 27 54 638.
To detect aerosols, gases, and vapors, such as hydrogen chloride, hydrogen fluoride, or sulfur dioxide, reaction products are produced in the preliminary layer that lead to a color in the following layer with known reagents for these reaction products.
To achieve a reliable indication of a color, the reaction products from the preliminary layer triggering the coloration must be gaseous. However, this also makes possible unhindered diffusion of the reaction products into the indicator layer, so that residual amounts of volatile components from the preliminary layer still pass over into the reagent layer even after completion of the measurement, and can thus subsequently distort the coloration in the indicator layer or even reverse it. For example, a preliminary layer impregnated with chromosulfuric acid and an indicator layer with an acid indicator (for example, Bromphenol Blue) are used to detect vinyl chloride. Hydrochloride acid is formed with the chromosulfuric acid under the action of the vinyl chloride, which leads to a coloration with the Bromphenol Blue in the indicator layer. Vinyl chloride also forms other decomposition products, such as chromyl chloride, with sulfuric acid. After completing the measurement, this chromyl chloride would diffuse through the porous interlayer into the indicator layer and lead to an additional coloration. The sulfuric acid of the preliminary layer can also withdraw from the reagent system the hydrochloric acid formed in the indicator layer, and thereby cause unstable behavior of the color after it is formed. It is then no longer possible to make a clear correlation between the degree of coloration and the amount of pollutant detected.
If the flow of the pollutant through the test tube is produced by a discontinuous pumping process from several individual pump strokes, diffusion of the components from the preliminary layer into the reagent layer must also be prevented n the period between the strokes. For example, if a test tube is to be used for the detection of methylene chloride, the preliminary layer is composed of potassium dichromate with concentrated sulfuric acid, impregnated on a carrier. The indicator layer includes palladium salt dissolved in water, that is also impregnated on a carrier. The methylene chloride is converted into carbon monoxide in the preliminary layer, which colors the palladium salt. The volatile water fraction must also not diffuse back into the preliminary layer during the dwell time between the successive pump strokes, since the concentrated sulfuric acid would become so very dilute that a reliable reaction of the pollutant to be detected to form carbon monoxide in the preliminary layer would be prevented.
When using the known system of preliminary layer and indicator layer, it is therefore impossible to achieve a reliable coloration of the indicator layer in all applications.